Imagine that you’re going to raise your hand. Maybe you are in class, or maybe you see a friend on the street and want to beckon him. How much time passes between the moment your brain sends the signal and your hand raises? Guess. 1 second? 1/10th of a second? 1/100th of a second?
What if I told you that it takes approximately -0,5 seconds? Yes, that’s right, the minus sign is not an error. According to an experiment conducted by Libet in the 80s, your body begins the movement 0,5 seconds before you make the conscious decision to move your hand.
Weird, right? Some people think this means free will is just an illusion, and our consciousness just a passenger watching events unfolding.